Abaqus Technology Brief
TB-05-WELD-1
Revised: April 2007
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Welding Simulation with Abaqus
Summary
Metal welding processes are employed in various industries. Gas welding techniques use the heat from a flame
to melt the parts to be joined and a filler material simultaneously. Extreme thermal loading is applied to the parts
being joined, and complex material responses are initiated. The steep, localized thermal gradients result in stress
concentrations in the welding zone. Consequently, modeling and simulation of welding processes are often complex and challenging. In this technology brief the use of
Abaqus for this class of problems is discussed and an
example analysis is presented.
Background
Welding is a fundamental manufacturing technique used
to join metal components. While there are a wide variety
of welding processes, most involve the application of heat
to induce coalescence of the metal in the adjoining parts.
The gas welding technique uses the heat from a gas
flame to melt together the contacting edges of the parts
being joined. A filler material may or may not be used.
The introduction of very high temperatures in the region of
the welded joint causes steep temperature gradients in
the structure. As a weld cools, residual stresses may be
produced in the weld zone; such stresses may cause the
structure to distort. The ability to predict the residual
stress state allows for the prediction of final part shapes
and a more complete understanding of how residual
stresses may affect the load capacity of a structure.
The finite element models described in this brief represent
structural beams. These structures are formed by welding
plate sections together, rather than producing the section
directly in a mill. The cross-sectional size of these components can make direct manufacture impractical.
Key Abaqus Features and Benefits
• Combined thermal-mechanical analysis procedures, in sequentially coupled or fully coupled
form
• Definition of transient heat sources and weld
material deposition via user subroutines
• Ability to specify complex thermal and mechanical material definitions, including temperature
and field variable dependence and latent heat
effects
The model is constructed using solid and shell elements.
A solid representation is used in the weld area to ensure
more accurate capture of the high solution gradients. Regions outside the weld zone, where thermal gradients are
not as severe, are modeled with shell elements to reduce
the overall model size. The transition between the shell
and solid regions is achieved using tied contact for the
thermal analysis and shell-to-solid coupling for the stress
analysis. The mesh is shown in Figure 1. The weld bead
is shown in red.
The techniques discussed herein are based on a generic
model but are transferable to a range of applications.
Finite Element Analysis Approach
The simulation uses a sequentially coupled approach in
which a thermal analysis is followed by a stress analysis.
The temperature results from the thermal analysis are
read into the stress analysis as loading to calculate the
thermal stress effects. The thermal analysis makes use
of Abaqus user subroutines DFLUX, GAPCON, and FILM.
The objective of the simulation is to predict post-weld deformation and residual stress distribution.
Figure 1: Mesh of the structure being welded
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Thermal Analysis Procedure
The thermal analysis is performed to calculate the heat
transfer resulting from the thermal load of the moving
torch. Three user subroutines are activated for the thermal analysis, as described below:
DFLUX:
In conclusion, Abaqus/Standard provides a set of general,
flexible modeling tools that allow for the prediction of residual stresses and final shapes in welded components.
Used to define the welding torch heat input as
a concentrated flux. The heat source travels
along the weld line to simulate the torch
movement.
GAPCON: Used to activate the conduction of heat between the deposited weld material and the
parent materials once the torch has passed a
given location.
FILM:
Similar to GAPCON in functionality, but used to
activate film coefficients to simulate convective ambient cooling once the torch passes a
given location.
Figure 2: Nodal temperatures in a typical region of the
weld as the torch traverses the weld line
The simulation is run as a fully transient heat transfer
analysis.
Structural Analysis Procedure
The structural analysis uses the thermal analysis
(temperature) results as the loading. The objective of the
structural analysis is to determine the stresses and strains
induced in the weld region during the cooling transient.
Boundary conditions are applied to restrain the system
against rigid body motion.
Results and Conclusion
Figure 3: Transient temperature profile at three points in
the torch path
Typical thermal results are shown in Figure 2, which displays a contour of nodal temperature as the torch travels
along the weld line.
The weld is initialized at 1800°C, but no heat is allowed to
transfer from the weld until the torch passes. As the torch
passes a given point on the weld line, the flux input is initiated, resulting in a localized increase in temperature to
over 2000°C.
In addition, as the torch passes the same weld line point,
conductive and convective heat transfer is activated,
causing a rapid drop in temperature as thermal energy is
transferred to the surrounding structure and environment.
Figure 4: Von Mises stress in the weld region at t=35 s.
Figure 3 shows the 35 s transient temperature profile at
three points close to the start of the torch path. The peak
temperature is reached when the torch is activated. A
sharp temperature drop is observed after the torch passes.
The stress response of the structure is driven by the high
thermal gradients. Figure 4 and Figure 5, respectively,
show plots of the von Mises stress and the effective plastic strain approximately 35 s into the process.
Figure 5: Effective plastic strain in the weld region at
t=35 s.
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Abaqus References
For additional information on the Abaqus capabilities referred to in this brief, see the following Abaqus 6.13 documentation references:
• Abaqus Analysis User’s Guide
- “Fully coupled thermal-stress analysis,” Section 6.5.3
• Abaqus User Subroutines Reference Guide
- “DFLUX,” Section 1.1.3
- “FILM,” Section 1.1.6
- “GAPCON,” Section 1.1.10
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